Large van-like containers which are commonly transported both by rail and by truck have been subjected to costly pilferage, particularly when on railroad cars. Such pilferage is largely committed by thieves who are relatives novices, and/or who are employees, whose presence in the vicinity is not a cause for suspicion. Such persons do not as a practical matter have heavy tools or equipment, or explosives, to aid in their criminal activities. Such thefts have been accomplished by breaking the relatively thin seals placed upon the conventional locking systems for the door or doors of such containers. The object of the present invention is to provide an improved, simple, low-cost locking system which is adequate to effectively deter such thievery, and which prevents opening the doors without the use of tools which cannot be carried by such a pilferer without the mere fact of possession of the tools revealing an intention to engage in an unusual or illegal activity.